Dehydration of diols using lithium phosphate catalyst

ABSTRACT

As a new dehydration catalyst for epoxides or diols, lithium phosphate having a ratio of the numbers of Li to P atoms between 2,2 and 3; a process for preparing the catalyst and its uses have also been disclosed.

il'nited States Patent 1191' Maurin 1 Sept. 11, 1973 4] DEIIYDRATION 0FDIOLS USING LITHIUM [56] 7 References Cited PHOSPHATE CATALYST UNITEDSTATES PATENTS {75] Inventor: Jean Maurin, Montivilliers, France1,841,055 1/1932 Reppe et al 260/681 3,391,214 7/1968 Fetterly 260/681[731 Assgneei cmflpagme Rmmage, 3,290,403 12/1966 Nemtsov et al. 260/681Pans, France 3,325,245 6 1967 Rowton 23 107 2,347,955 5 1944 Korpi 252437 [22] 1972 2,986,585 5 1961 Denton 260/632 211 App], No; 245,7933,510,537 5/1970 Sheng et al. 260/681 Related U.S. Application DataDivision of Ser. No. 30,276, April 20, 1970, abandoned.

Primary ExaminerDelbert E. Gantz Assistant Examiner-C. Ev SpresserAtt0rneyA. Thomas S. Safford ABSTRACT As a new dehydration catalyst forepoxides or diols, lithium phosphate having a ratio of the numbers of Lito P atoms between 2,2 and 3; a process for preparing the catalyst andits uses have also been disclosed.

3 Claims, No Drawings DEHYDRATION F DIOLS USING LITHIUM PHOSPHATECATALYST This is a Division of application Ser. No. 30,276, filed Apr.20, 1970 now abandoned.

This invention relates to a new dehydration catalyst; more particularlyto a lithium phosphate catalyst. Further, this invention also relates toa method of preparing the catalyst as well as the use of this catalystfor the dehydration of diols and epoxides to dienes.

The catalytic properties of lithium phosphate, 3 O4, in reactions ofisomerization of epoxides in olefin alcohols are well known to thoseskilled in the art and the users of this catalyst for the conversion ofepoxides into corresponding diolefins by isomerization of the epoxideinto alcohol and the dehydration of said alcohol to form diolefin havealready been described in the literature. In the employment of thecatalyst, the isomerization and dehydration may, in particular becarried out simultaneously in the, presence of lithium phosphate, whichthen acts as isomerization-dehydration catalyst.

It has been found unexpectedly that the catalytic properties of lithiumphosphate in these isomerization reactions are closely related to themethod of preparation of this compound. In particular, while the factthat the catalyst is customarily prepared in a basic medium by reactingan excess of lithium hydroxide with phosphoric acid, i.e. using areaction mixture in which the ratio of the numbers of Li/P atoms isgreater than 3, it has neither been known nor appreciated nor beenforeseeable that below this threshold value, the lithium phosphateobtained constitutes a remarkable dehydration catalyst whose isomerizingproperties are minimized in substantial degree.

The present invention has therefore as its object adehydration catalystcomprising lithium phosphate prepared from phosphoric acid and lithiumhydroxide under reaction conditions such that the ratio of the numbersof Li]? atoms of the reaction medium is between 2.2 and 3, andpreferably between 2.4 and 2.9.

Another object of the invention is the method of pre-' paring thiscatalyst.

As this method is particularly well adapted as will be noted from thedescription given below for the dehydration of a diol to a diene and theselective dehydration of an epoxide to diene, the invention has as itsobject also the use of this catalyst in thesespecific de hydrationreactions. I

In a preferred embodiment of the method of preparing the catalyst inaccordance with the invention, one starts by reacting phosphoric acidwith a solution of lithium hydroxide in proportions such that thephosphate l.iH-1l().| is formed. The solution obtained is then mixed,while cold, with lithium hydroxide, in solution, in proportions suchthat the ratio of the numbers of Li/P atoms in the reaction medium isbetween 2.2 and 3, and preferably between 2.4 and 2.9. The precipitatcdphosphoate l.i,-,l0.1 is allowed to settle out and after removal of theliquid phase the precipitate is dried and calcined at 300C. When thecatalyst is prepared in the indicated manner, there is substantially nocon tamination by co-ions such as sodium or nitrates. Hence, thecatalyst product performance can easily be controlled.

This method of preparation, although the preferred method, does not,however, constitute any limitation. on the invention and the testscarried out by the appli cant have proven that the lithium phosphateprepared in a single phase by direct mixing of the reagents hassubstantially equivalent catalytic activity, this activity and theselectivity of the catalyst depending essentially on the ratio of thenumber of Li/P atoms in the reaction medium for the preparation of thecatalyst.

This will be evident from the following examples which are in no waylimitative and which are directed merely at illustrating the applicationof the catalyst of the invention to the dehydration of epoxides anddiols to dienes.

EXAMPLE I A number of catalysts are prepared corresponding todifferentvalues of the ratio of the number of Li/P atoms of thepreparation reaction medium by the following method: 123 g of LiOH.H2Oare dissolved in 659 m1 of water. To a third of this solution there areadded X grams of 86 percent phosphoric acid 1 (HQPO4) contained in 20 mlof water. To this cooled solution 90 g of ice are added, while 200 g ofice are added to the unused two-thirds of the lithium hydroxidesolution. Thetwo solutions are cooled until their temperature reaches2C; the LiH PO4 solution is then rapidly mixed with the lithiumhydroxide solution. The suspension is diluted to a volume of 4,000 ml;it is set aside for 12 hours. The precipitate is recovered and dried atl 10C.

Four catalysts are prepared by using respectively as value 'for X:115.6, 111.3, 104.4 and 98 grams of 86% H -,PO these catalystscorrespond to a ratio of the number of Li/P atoms in the reactionmixture of 2.8, 3, 3.2 and 3.4 respectively.

Each catalyst is crushed into pieces of about 1 to 2 mm diameter andseveral glass tubes are filled with 10 cc of these catalysts. Each tubeis brought to 300C and is fed with methyl epoxy 2,.3-butane diluted innitrogen at a rate of flow of 10 cc/hr for the epoxide .and 3 1/hr forthe nitrogen. Table I below gives the composition in percent by weightof the mixture obtained at the outlet of the'tube for each catalyst. Theanalysis of this composition was carried out by gas phase chromatographyand the numbers indicated correspond to the percentages of the ares ofthe chromatographic peaks.

The comparison of the results obtained with the use of the differentcatalysts shows a far better formation of isoprene by dehydration ofmethyl-epoxy 2,3- butane on Li,P0,when the catalyst has been formed in areac tion medium in which the Lil? ratio is equal to 2.8; it should alsobe noted that the use of this catalyst is ac companied only by a smallquantitative change of the carbon structure of the initial epoxide,contrary to the other catalysts. Thus it is noted that the carbon struc-EXAMPLE 11 The catalysts of Example I, (and 3 others for which the valueof X is respectively: 128.0, 138.9 and 151.5 grams, corresponding to aLi/P ratio of 2.6, 2.4 and 2.2) are used to carry out the dehydration ofmethylbutane-diol-2,3 into isoprene under the same operating conditionsbut at a temperature of 400C.

Table 11 below gives the composition in percent by weight of the mixtureobtained at the outlet of the tube for each catalyst. Analysis of thiscomposition was effected by the method explained in Example I.

charge of 63.3 percent and 80.3 percent is obtained, a yield ofcompounds having a carbonyl function is 43.1 percent and 29.3 percentrespectively and a yield of isoprene is 0 percent.

The use of the catalyst in accordance with the inven tion isparticularly advantageous within a process in which an olefin isoxidized into epoxide or diol in order subsequently to obtain adiolefin. As a matter of fact, this catalyst gives only by-productssited on the same carbon, and particularly a ketonic, carbonyl structurewhich is possible to reconvert to the initial olefin, i.e., recycle, byreduction and dehydration, while, on the contrary, any product whosestructure has been isomerized must be eliminated from the system andtherefore constitutes a final loss.

The catalysts in accordance with the invention have the advantage thatthese can be calcined at .about 600C without losing their activity sothat these can be regenerated after use.

What is claimed is:

1.1n a method of dehydrating a vicinal diol to a diene the improvementconsisting essentially of dehydrating said vicinal diol in the presenceof lithium phosphate as a catalyst therefor, prepared from phosphoricacid and T TA iLE ft Lil? ratio of the preparation reaction mediumConversion of the charge lsoprcnc 48. 5 62. 1 64. 0 55. 3 1. 7 3. 6 1. 0D Mathyl-cpoxy-2,3-butnnc 0. 1 3. 5 3. 3 Methyl isopropyl ketonc 29. 429. 8 29. 4 25.7 22. 2 24. 4 24. 4 Dimcthyl vinyl carhinol 0.7 0.7 0.5lVlcthyl-2l ut.cn-l-ol-3 14. 8 0. G 14. 2 18. 2 11. 1 8. 7 M ethyl-241ydroxy-ZJmtanonc 2. 7 l5. 8 21. 2 'lrimcthylacctaldchydc 4. 1 5. 1 4. 13. 3 23. 2 13. 3 10. 0 Dimcthyl-Z-Z-propanol-l 4. 4 18. 8 22. 9Miscellaneous 2. 5 1. 8 -1. 9 1. 5 6. 9 8. 8 8.0

Table 11 shows that the catalysts of the invention, that is to say,those one for which the Li/P ratio of the reaction medium is comprisedbetween 2.2 and 3.0, produces the greatest conversion of themethyl-butanediol-2-3; these catalysts have the greatest effectivenessfor the dehydration of this charge into isoprene; finally, they havelittle isomerizing effect.

It should be noted by way of comparison that with a conventionaldehydration catalyst such as boron phosphate or thorium dioxide, a verysubstantial isomerization is observed whereby the charge isomerizes intocompounds having a carbonyl function. Thus by separately passingmethyl-epoxy-2,3-butane and methylbutane-diol-2,3 at 350C over thoriumdioxide with an hourly space velocity of l, a conversion rate of thelithium hydroxide such that the ratio of the number of Li/P atoms in thereaction medium is between 2.2 and 3.

2. The method according to claim 1 and wherein the I diol is methylbutane diol 2,3.

and recovering the catalyst.

2. The method according to claim 1 and wherein the diol is methyl butanediol -2,3.
 3. The method according to claim 1 and wherein the catalystis prepared by reacting phosphoric acid and lithium hydroxide with eachother in a reaction solution, said reaction solution is cooled, furtherreacting the cooled reaction solution with an additional amount ofcooled lithium hydroxide to obtain a lithium phosphate such that theratio of the number of Li/P atoms of the amounts of lithium hydroxideand phosphoric acid used in the reaction mixture is between 2.2 and 3,and recovering the catalyst.